Field of the Invention
The present invention relates to a spirally-wound lithium battery using lithium metal or lithium alloy for an anode.
Description of the Related Art
A lithium battery using lithium metal or lithium alloy for an anode active material includes: a primary battery using manganese dioxide, copper oxide, or the like for a cathode active material, and a secondary battery using lithium cobalt composite oxide (LiCoO2) or the like for a cathode active material. The lithium battery has a configuration in which a battery can is filled with an electrode body comprising a cathode material including the cathode active material and an anode material including the anode active material, arranged to be opposed to each other via a separator, together with a non-aqueous organic electrolyte, and such an outer case filled therewith is sealed. Note that although lithium batteries have various types depending on the configurations of its outer body and its electrode body, a spirally-wound lithium battery, which is configured such that a wound electrode body is stored in a bottomed cylindrical battery can (hereinafter, also referred to as an anode can) serving also as an anode current collector, will be described in present embodiments.
FIG. 1 illustrates an outline configuration of a spirally-wound lithium battery 1. The spirally-wound lithium battery 1 illustrated in FIG. 1 includes a bottomed cylindrical anode can 2. FIG. 1 is a longitudinal sectional view illustrating the spirally-wound lithium battery 1 when the extending direction of the cylindrical axis 50 in the anode can 2 is set as an up-and-down (longitudinal) direction, with the bottom of the anode can 2 being arranged downward. The spirally-wound lithium battery 1 stores, in the anode can 2, a cathode 3, an anode 4, a separator 5, and a non-aqueous organic electrolyte 30, as power generation elements. Further, the spirally-wound lithium battery 1 has such a basic configuration that an opening of the anode can 2 is sealed with a sealing body 20.
The cathode 3 configuring the power generation elements is obtained such that, for example, a stainless steel lath is coated with a cathode material in a slurry form, cut into a predetermined size and then dried. The anode 4 is made of lithium metal or a lithium alloy in a plate form (hereinafter, also referred to as a lithium anode 4). Then, the lithium anode 4 and the cathode 3 are arranged in such a manner as to be opposed to each other via the separator 5 made of, for example, a microporous polyolefin film, thereby configuring a strip-shaped electrode body 10, and the strip-shaped electrode body 10 is inserted in the anode can 2 in a wound state.
In the spirally-wound lithium battery 1 given here, the sealing body 20 includes a sealing plate 6, a positive terminal 7, a metal washer 8, and a sealing gasket 9. The sealing plate 6 is in a disk shape with an opening provided at the center thereof, and the edge of the disk is bent upward. In the central opening of the sealing plate 6, the metal positive terminal 7 and the metal washer 8 are swaged via the resin sealing gasket 9. Then, the edge of the sealing plate 6 and the upper edge of the anode can 2 are laser welded (at the position of the reference numeral 51 in the figure). Thus, the opening of the anode can 2 is sealed and the anode can 2 is hermetically sealed. Further, a cathode current collector and the lower surface of the positive terminal 7 are coupled to each other via a positive electrode tab 11, and the lithium anode 4 and the inner surface of the anode can 2 are coupled to each other via an anode tab 12. And, the hermetically sealed anode can 2 is filled with the non-aqueous organic electrolyte 30 obtained by dissolving lithium salt in a non-aqueous solvent. Note that the related technology is described in Japanese patent publication No. 5252691 below. Further, configuration of various lithium primary batteries are described in FDK Corporation, “lithium battery”, [online], [Searched on Sep. 7, 2013], Internet <URL: http://www.fdk.co.jp/battery/lithium/index.html>.
Regardless of configurations, in a lithium battery, lithium anode is being dissolved with discharge. Then, in a spirally-wound lithium battery using an anode can, there is such a problem called “lithium break” that a lithium anode may crack or break in a discharge ending stage in some cases. That is, the lithium anode physically “breaks”. If the lithium anode cracks, internal resistance increases. If the lithium anode breaks, the area thereof in which the lithium anode is not electrically connected to the anode tab would not contribute to power generation at all, resulting in substantial decrease in battery capacity.
In the technique disclosed in the above Japanese patent publication No. 5252691, anode current collectors are certainly stacked on one surface of a wound lithium anode, and it is described that “the anode current collectors has a width equal or greater than the width of a metallic lithium foil or lithium alloy foil, and a greater length, and this can avoid metallic lithium foil or lithium alloy foil from breaking along the circumference of the anode current collector and being electrically disconnected.” However, in the technique described in Japanese patent publication No. 5252691, the initial internal resistance is large or voltage may greatly drop in the discharge ending stage.